Abstract:
The IPY long-run data were obtained from the European
Incoherent Scatter Svalbard radar (ESR) observations during March
2007 and February 2008. Since the solar and geomagnetic activities
were quite low during the period, this data set is extremely
helpful for describing the basic states (ground states) of the
thermosphere and ionosphere in the polar cap region. The
monthly-averaged ion temperatures for 12 months show similar local
time (or UT) variations to each other. The ion temperatures also
show significant seasonal variations. The amplitudes of the local
time and seasonal variations observed are much larger than the ones
predicted by the IRI-2007 model. In addition, we performed
numerical simulations with a general circulation model (GCM), which
covers all the atmospheric regions, to investigate variations of the
neutrals in the polar thermosphere. The GCM simulations show
significant variations of the neutral temperature in the polar
region in comparison with the NRLMSISE-00 empirical model. These
results indicate that both the ions and neutrals would show larger
variations than those described by the empirical models, suggesting
significant heat sources in the polar cap region even under
solar minimum and geomagnetically quiet conditions.
Key words:
Polar cap, ionosphere, thermosphere, EISCAT radar, GCM, simulation, IPY, solar minimum.